northern oak fern vs limestone fern

northern oak fern and limestone fern both are nouns.

Word	Noun	Adjective	Verb	Adverb
northern oak fern	Yes	No	No	No
limestone fern	Yes	No	No	No

As nouns, northern oak fern and limestone fern are synonyms defined as:

northern oak fern and limestone fern: yellow-green fern of rocky areas of Northern Hemisphere

Other synonyms of northern oak fern include Gymnocarpium robertianum.

northern oak fern (noun)	limestone fern (noun)
yellow-green fern of rocky areas of Northern Hemisphere	yellow-green fern of rocky areas of Northern Hemisphere